Lymphocytes isolated from a subject (e.g. patient) can be activated in vitro and genetically modified to express synthetic proteins that enable redirected engagement with other cells and environments based upon the genetic programs incorporated. An example of such a synthetic protein is a chimeric antigen receptor (CAR). One CAR that is currently used is a fusion of an extracellular recognition domain (e.g., an antigen-binding domain), a transmembrane domain, and one or more intracellular signaling domains encoded by a replication incompetent retrovirus.
While retroviruses have shown efficacy in infecting non-dividing cells, resting CD4 and CD8 lymphocytes are refractory to genetic transduction by these vectors. To overcome this difficulty, these cells are typically activated in vitro using stimulation reagents before genetic modification with the CAR gene vector can occur. Following stimulation and transduction, the genetically modified cells are expanded in vitro and subsequently reintroduced into a lymphodepleted patient. Upon antigen engagement in vivo, the intracellular signaling portion of the CAR can initiate an activation-related response in an immune cell and release of cytolytic molecules to induce tumor cell death.
Such current methods require extensive manipulation and manufacturing of proliferating T cells outside the body prior to their reinfusion into the patient, as well as lymphodepleting chemotherapy to free cytokines and deplete competing receptors to facilitate T cell engraftment. Such CAR therapies further cannot be controlled for propagation rate in vivo once introduced into the body, nor safely directed towards targets that are also expressed outside the tumor. As a result, CAR therapies today are typically infused from cells expanded ex vivo from 12 to 28 days using doses from 1×105 to 1×108 cells/kg and are directed towards targets, for example tumor targets, for which off tumor on target toxicity is generally acceptable. These relatively long ex vivo expansion times create issues of cell viability and sterility, as well as sample identity in addition to challenges of scalability. Thus, there are significant needs for a safer, more effective scalable T cell or NK cell therapy.